Heavy distortion on an analog audio signal creates a pseudo-square wave that CMOS digital circuits can process as a clock signal

An ordinary analog audio signal (CD player, guitar) swings with smooth, curved waveforms at about 1V peak-to-peak. CMOS digital circuits snap between 0V and 9V and treat signals above a threshold as ‘1’ and below as ‘0.’ With enough gain and cascaded distortion stages, the rounded peaks and troughs of the audio waveform get clipped into something approaching the sharp edges of a digital square wave. This can trigger CMOS circuits like the CD4093 gated oscillator or CD4040 binary divider, letting audio pitch control circuit behavior. A distorted guitar playing a melody will drive the divider’s clock, producing sub-octave notes tracking the guitar. This is Collins’ ‘Fuzzy Dicer’ and ‘Low Rider’ circuit family.

Examples

Cascade three CD4049 stages with high gain, plug guitar, output through CD4040 divider: each division output tracks the guitar’s pitch one or more octaves lower. Slowly picking notes produces single subharmonics; chords produce complex rhythmic patterns.

Assessment

Why does distortion help interface an analog audio signal to a CMOS digital circuit? What would happen if you connected a clean (undistorted) CD player output directly to the clock input of a CD4040?